Active metal / aqueous electrochemical cells and systems

ABSTRACT

Alkali (or other active) metal battery and other electrochemical cells incorporating active metal anodes together with aqueous cathode/electrolyte systems. The battery cells have a highly ionically conductive protective membrane adjacent to the alkali metal anode that effectively isolates (de-couples) the alkali metal electrode from solvent, electrolyte processing and/or cathode environments, and at the same time allows ion transport in and out of these environments. Isolation of the anode from other components of a battery cell or other electrochemical cell in this way allows the use of virtually any solvent, electrolyte and/or cathode material in conjunction with the anode. Also, optimization of electrolytes or cathode-side solvent systems may be done without impacting anode stability or performance. In particular, Li/water, Li/air and Li/metal hydride cells, components, configurations and fabrication techniques are provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/649,245 filed Dec. 29, 2009, titled ACTIVE METAL/AQUEOUSELECTROCHEMICAL CELLS AND SYSTEMS, now pending; which is a continuationof U.S. patent application Ser. No. 11/824,548 filed Jun. 29, 2007,titled ACTIVE METAL/AQUEOUS ELECTROCHEMICAL CELLS AND SYSTEMS, nowissued as U.S. Pat. No. 7,666,233; which is a divisional of U.S. patentapplication Ser. No. 10/772,157 filed Feb. 3, 2004, titled ACTIVEMETAL/AQUEOUS ELECTROCHEMICAL CELLS AND SYSTEMS, now issued as U.S. Pat.No. 7,645,543, which claims priority to U.S. Provisional PatentApplication No. 60/511,710 filed Oct. 14, 2003, titled IONICALLYCONDUCTIVE COMPOSITES FOR PROTECTION OF ACTIVE METAL ELECTRODES INCORROSIVE ENVIRONMENTS; U.S. Provisional Patent Application No.60/518,948 filed Nov. 10, 2003, titled BI-FUNCTINALLY COMPATIBLEIONICALLY COMPOSITES FOR ISOLATION OF ACTIVE METAL ELECTRODES IN AVARIETY OF ELECTROCHEMICAL CELLS AND SYSTEMS; U.S. Provisional PatentApplication No. 60/527,098 filed Dec. 3, 2003, titled ACTIVE METAL/METALHYDRIDE BATTERY CELL; U.S. Provisional Patent Application No. 60/536,688filed Jan. 14, 2004, titled ACTIVE METAL/WATER BATTERY CELLS; U.S.Provisional Patent Application No. 60/526,662 filed Dec. 2, 2003, titledACTIVE METAL/AIR BATTERY CELL; and U.S. Provisional Patent ApplicationNo. 60/536,689 filed Jan. 14, 2004, titled PROTECTED ACTIVE METALELECTRODES FOR USE IN ACTIVE METAL/AQUEOUS ELECTROLYTE BATTERY CELLS.

The benefit of each of these prior applications is claimed, and each ofthese prior applications is incorporated herein by reference in itsentirety and for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to active metal electrochemicaldevices. More particularly, this invention relates to activemetal/aqueous (e.g., lithium) battery cells made possible by activemetal electrode structures having ionically conductive membranes forprotection of the active metal from deleterious reaction with air,moisture and other battery cell components, methods for theirfabrication and applications for their use.

2. Description of Related Art

The low equivalent weight of alkali metals, such as lithium, render themparticularly attractive as a battery electrode component. Lithiumprovides greater energy per volume than the traditional batterystandards, nickel and cadmium. Unfortunately, no rechargeable lithiummetal batteries have yet succeeded in the market place.

The failure of rechargeable lithium metal batteries is largely due tocell cycling problems. On repeated charge and discharge cycles, lithium“dendrites” gradually grow out from the lithium metal electrode, throughthe electrolyte, and ultimately contact the positive electrode. Thiscauses an internal short circuit in the battery, rendering the batteryunusable after a relatively few cycles. While cycling, lithiumelectrodes may also grow “mossy” deposits that can dislodge from thenegative electrode and thereby reduce the battery's capacity.

To address lithium's poor cycling behavior in liquid electrolytesystems, some researchers have proposed coating the electrolyte facingside of the lithium negative electrode with a “protective layer.” Suchprotective layer must conduct lithium ions, but at the same time preventcontact between the lithium electrode surface and the bulk electrolyte.Many techniques for applying protective layers have not succeeded.

Some contemplated lithium metal protective layers are formed in situ byreaction between lithium metal and compounds in the cell's electrolytethat contact the lithium. Most of these in situ films are grown by acontrolled chemical reaction after the battery is assembled. Generally,such films have a porous morphology allowing some electrolyte topenetrate to the bare lithium metal surface. Thus, they fail toadequately protect the lithium electrode.

Various pre-formed lithium protective layers have been contemplated. Forexample, U.S. Pat. No. 5,314,765 (issued to Bates on May 24, 1994)describes an ex situ technique for fabricating a lithium electrodecontaining a thin layer of sputtered lithium phosphorus oxynitride(“LiPON”) or related material. LiPON is a glassy single ion conductor(conducts lithium ion) that has been studied as a potential electrolytefor solid state lithium microbatteries that are fabricated on siliconand used to power integrated circuits (See U.S. Pat. Nos. 5,597,660,5,567,210, 5,338,625, and 5,512,147, all issued to Bates et al.).

Work in the present applicants' laboratories has developed technologyfor the use of glassy or amorphous protective layers, such as LiPON, inactive metal battery electrodes. (See, for example, U.S. Pat. No.6,025,094, issued Feb. 15, 00, U.S. Pat. No. 6,402,795, issued Jun. 11,02, U.S. Pat. No. 6,214,061, issued Apr. 10, 01 and U.S. Pat. No.6,413,284, issued Jul. 02, 02, all assigned to PolyPlus BatteryCompany).

Prior attempts to use lithium anodes in aqueous environments reliedeither on the use of very basic conditions such as use of concentratedaqueous KOH to slow down the corrosion of the Li electrode, or on theuse of polymeric coatings on the Li electrode to impede the diffusion ofwater to the Li electrode surface; in all cases however, there wassubstantial reaction of the alkali metal electrode with water. In thisregard, the prior art teaches that the use of a aqueous cathodes orelectrolytes with Li-metal anodes is not possible since the breakdownvoltage for water is about 1.2 V and a Li/water cell can have a voltageof about 3.0 V. Direct contact between lithium metal and aqueoussolutions results in violent parasitic chemical reaction and corrosionof the lithium electrode for no useful purpose. Thus, the focus ofresearch in the lithium metal battery field has been squarely on thedevelopment of effective non-aqueous (mostly organic) electrolytesystems.

SUMMARY OF THE INVENTION

The present invention concerns alkali (or other active) metal batterycells and electrochemical cells incorporating them together with aqueouscathode/electrolyte systems. The battery cell negative electrode (anode)has a highly ionically conductive (at least about 10⁻⁷ S/cm, and morepreferably at least 10⁻⁶ S/cm, for example 10⁻⁵ S/cm to 10⁻⁴ S/cm, andas high as 10⁻³ S/cm or higher) protective membrane adjacent to thealkali metal anode that effectively isolates (de-couples) the alkalimetal electrode from solvent, electrolyte processing and/or cathodeenvironments, including such environments that are normally highlycorrosive to Li or other active metals, and at the same time allows iontransport in and out of these potentially corrosive environments. Theprotective membrane is thus chemically compatible with active metal(e.g., lithium) on one side and a wide array of materials, includingthose that are normally highly corrosive to Li or other active metals onthe other side, while at the same time allowing ion transport from oneside to the other. In this way, a great degree of flexibility ispermitted the other components of an electrochemical device, such as abattery cell, made with the protected active metal electrodes. Isolationof the anode from other components of a battery cell or otherelectrochemical cell in this way allows the use of virtually anysolvent, electrolyte and/or cathode material in conjunction with theanode. Also, optimization of electrolytes or cathode-side solventsystems may be done without impacting anode stability or performance.

Such a protected active metal anode may be used with a wide array ofsolvents, electrolytes and cathode materials (including those morestable in lithium metal systems, such as are used in lithium-sulfurbattery systems described in the patents of PolyPlus Battery Company,for example, U.S. Pat. No. 6,025,094, issued Feb. 15, 00, U.S. Pat. No.6,402,795, issued Jun. 11, 02, U.S. Pat. No. 6,214,061, issued Apr. 10,01 and U.S. Pat. No. 6,413,284, issued Jul. 02, 02, and U.S. patentapplication Ser. No. 10/686,189, filed Oct. 14, 03, each of which isincorporated by reference herein in its entirety for all purposes); andmore Li-corrosive materials including air, ionic (including protic)solutions, aqueous electrolytes, molten salts, and ionic liquids, forexample, operating conditions (including high through low temperatures)and discharge rate regimes (including high through low discharge rates).Li anode corrosion is not an issue and the electrolyte compatibilitywith the anode is not a concern. A few examples of desirable batterycells in accordance with the present invention include Li-air;Li-aqueous electrolyte; and Li-sea/salt water. Other novel and usefulelectrochemical devices are also rendered possible in accordance withthe present invention, as described further below. The use of cathodematerials extremely reactive with Li is also possible by usingprotective composites in accordance with the present invention, forexample PbSnF₄ and the like, for Li/F batteries.

The present invention uses ionically conductive membranes for decouplingthe active metal anode and cathode sides of an active metalelectrochemical cell. The membranes may be incorporated in active metalnegative electrode (anode) structures and electrochemical devices andcomponents, including batteries and fuel cells. The membranes are highlyconductive for ions of the active metal, but are otherwise substantiallyimpervious. They are chemically stable on one side to the active metalof the anode (e.g., lithium), and on the other side to the cathode,other battery cell components such as solid or liquid phaseelectrolytes, including organic or aqueous liquid electrolytes, andpreferably to ambient conditions. The membrane is capable of protectingan active metal anode from deleterious reaction with other batterycomponents or ambient conditions and decoupling the chemicalenvironments of the anode and cathode enabling use of anode-incompatiblematerials, such as solvents and electrolytes, on the cathode sidewithout deleterious impact on the anode, and vice versa. This broadensthe array of materials that may be used in active metal electrochemicalcells and facilitates cell fabrication while providing a high level ofionic conductivity to enhance performance of an electrochemical cell inwhich the membrane is incorporated.

It is widely known that lithium metal reacts violently with water, andeven more violently with aqueous acidic solutions. However, it has beenfound that a cell composed of a lithium electrode protected with a LiPON(Ag)/OHARA glass-ceramic composite in accordance with the presentinvention, as described above, can be immersed into acidic aqueouselectrolytes without incident. The thermodynamic open circuit potentialis observed vs. a Ag/AgCl reference and a normal hydrogen electrode andlithium can be discharged into the aqueous electrolyte causing hydrogenevolution to occur at a Pt counter electrode, with no evidence ofcorrosion or chemical reaction at the lithium electrode. It has beenfurther shown that such a protected lithium electrode can be immersedinto an aqueous bath having dissolved LiOH, and the lithium electrodecan be reversibly cycled in such an aqueous electrolyte. Priorexperiments showing these results are unknown, as corrosion of metalliclithium in aqueous environments is known to rapidly occur. Thisdiscovery enables a number of unique battery systems to be developed,including Li/water and Li/air batteries. These systems have beenattempted previously using unprotected lithium metal electrodes.However, due to the rapid corrosion of unprotected lithium metalelectrodes in water, batteries formed using such electrodes would havevery short life, and have limited commercial appeal due to safetyproblems. With the current invention, the protected lithium electrodeshows no evidence of corrosion/chemical reaction with aqueouselectrolytes, and results in batteries that should have wide commercialappeal.

In various aspects, the invention relates to an active metal/aqueousbattery cell. The battery cell includes an active metal anode having afirst surface and a second surface; a cathode structure with anelectronically conductive component, an ionically conductive component,and an electrochemically active component. At least one cathodestructure component comprises an aqueous constituent. An ionicallyconductive protective membrane is disposed on the first surface of theanode, the membrane having one or more materials configured to provide afirst surface chemically compatible with the active metal of the anodein contact with the anode, and a second surface substantially imperviousto and chemically compatible with the cathode structure and in contactwith the cathode structure.

Exemplary cells in accordance with the present invention includeLi/water, Li/air and Li/metal hydride batter cells and otherelectrochemical cells.

The invention also provides a variety of cell and component fabricationtechniques, cell components and configurations.

These and other features of the invention are further described andexemplified in the detailed description below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an active metal battery cellincorporating an ionically conductive protective membrane in accordancewith the present invention.

FIGS. 2A and B are a schematic illustrations of ionically conductiveprotective membrane battery separators in accordance with the presentinvention.

FIG. 3A is a schematic illustration of an active metal anode structureincorporating an ionically conductive protective laminate compositemembrane in accordance with the present invention.

FIG. 3B is a schematic illustration of an active metal anode structureincorporating an ionically conductive protective graded compositemembrane in accordance with the present invention.

FIGS. 4A-B, 5 and 6A-B are schematic illustrations of alternativemethods of making an electrochemical device structure incorporating anionically conductive protective membrane in accordance with the presentinvention.

FIG. 7 illustrates a specific implementation of a lithium/water batterycell in accordance with the present invention.

FIG. 8 illustrates a lithium/air battery cell in accordance with thepresent invention.

FIG. 9 illustrates a lithium/metal hydride battery cell in accordancewith one embodiment of the present invention.

FIG. 10 illustrates a Li/water battery and hydrogen generator for a fuelcell in accordance with one embodiment of the present invention.

FIG. 11 depicts the fabrication of a thin-film Li/water or Li/airbattery using plasma-spray and other deposition techniques in accordancewith one embodiment of the present invention.

FIGS. 12A-E illustrate a technique for fabricating thin glass orglass-ceramic protective membranes attached to an electronicallyconductive porous support suitable for use in active metal/aqueous cellsin accordance with one embodiment of the present invention.

FIG. 13 shows an embodiment in accordance with the present invention inwhich a plurality of glass, ceramic or glass-ceramic ionicallyconductive protective membrane plates are bonded into an array byelastomeric seals.

FIG. 14 illustrates a tubular construction embodiment of a Li/water orLi/air cell in accordance with the present invention.

FIG. 15 illustrates a capillary construction embodiment of a Li/water orLi/air cell in accordance with the present invention.

FIG. 16 illustrates a protected lithium electrode used as the cell ofExample 1.

FIGS. 17-27 are plots of data illustrating the performance of variouscells incorporating anodes with ionically conductive protectivemembranes and aqueous-containing cathodes in accordance with the presentinvention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Reference will now be made in detail to specific embodiments of theinvention. Examples of the specific embodiments are illustrated in theaccompanying drawings. While the invention will be described inconjunction with these specific embodiments, it will be understood thatit is not intended to limit the invention to such specific embodiments.On the contrary, it is intended to cover alternatives, modifications,and equivalents as may be included within the spirit and scope of theinvention as defined by the appended claims. In the followingdescription, numerous specific details are set forth in order to providea thorough understanding of the present invention. The present inventionmay be practiced without some or all of these specific details. In otherinstances, well known process operations have not been described indetail in order not to unnecessarily obscure the present invention.

When used in combination with “comprising,” “a method comprising,” “adevice comprising” or similar language in this specification and theappended claims, the singular forms “a,” “an,” and “the” include pluralreference unless the context clearly dictates otherwise. Unless definedotherwise, all technical and scientific terms used herein have the samemeaning as commonly understood to one of ordinary skill in the art towhich this invention belongs.

Introduction

The present invention concerns alkali (or other active) metal batterycells and electrochemical cells incorporating them together with aqueouscathode/electrolyte systems. The battery cell negative electrode (anode)has a highly ionically conductive (at least about 10⁻⁷ S/cm, and morepreferably at least 10⁻⁶ S/cm, for example 10⁻⁵ S/cm to 10⁻⁴ S/cm, andas high as 10⁻³ S/cm or higher) protective membrane adjacent to thealkali metal anode that effectively isolates (de-couples) the alkalimetal electrode from solvent, electrolyte processing and/or cathodeenvironments, including such environments that are normally highlycorrosive to Li or other active metals, and at the same time allows iontransport in and out of these potentially corrosive environments. Theprotective membrane is thus chemically compatible with active metal(e.g., lithium) on one side and a wide array of materials, includingthose including those that are normally highly corrosive to Li or otheractive metals on the other side, while at the same time allowing iontransport from one side to the other. In this way, a great degree offlexibility is permitted the other components of an electrochemicaldevice, such as a battery cell, made with the protected active metalelectrodes. Isolation of the anode from other components of a batterycell or other electrochemical cell in this way allows the use ofvirtually any solvent, electrolyte and/or cathode material inconjunction with the anode. Also, optimization of electrolytes orcathode-side solvent systems may be done without impacting anodestability or performance.

Such a protected active metal anode may be used with a wide array ofsolvents, electrolytes and cathode materials (including those morestable in lithium metal systems, such as are used in lithium-sulfurbattery systems described in the patents of PolyPlus Battery Company,for example, U.S. Pat. No. 6,025,094, issued Feb. 15, 00, U.S. Pat. No.6,402,795, issued Jun. 11, 02, U.S. Pat. No. 6,214,061, issued Apr. 10,01 and U.S. Pat. No. 6,413,284, issued Jul. 02, 02, and U.S. patentapplication Ser. No. 10/686,189, filed Oct. 14, 03, each of which isincorporated by reference herein in its entirety for all purposes); andmore Li-corrosive materials including air, ionic (including protic)solutions, aqueous electrolytes, molten salts, and ionic liquids, forexample), operating conditions (including high through low temperatures)and discharge rate regimes (including high through low discharge rates).Li anode corrosion is not an issue and the electrolyte compatibilitywith the anode is not a concern. A few examples of desirable batterycells in accordance with the present invention include Li-air;Li-aqueous electrolyte; and Li-sea/salt water. Other novel and usefulelectrochemical devices are also rendered possible in accordance withthe present invention, as described further below. The use of cathodematerials extremely reactive with Li is also possible by usingprotective composites in accordance with the present invention, forexample PbSnF₄ and the like, for Li/F batteries.

The present invention uses ionically conductive membranes for decouplingthe active metal anode and cathode sides of an active metalelectrochemical cell. The membranes may be incorporated in active metalnegative electrode (anode) structures and electrochemical devices andcomponents, including battery and fuel cells. The membranes are highlyconductive for ions of the active metal, but are otherwise substantiallyimpervious. They are chemically stable on one side to the active metalof the anode (e.g., lithium), and on the other side to the cathode,other battery cell components such as solid or liquid phaseelectrolytes, including organic or aqueous liquid electrolytes, andpreferably to ambient conditions. The membrane is capable of protectingan active metal anode from deleterious reaction with other batterycomponents or ambient conditions and decoupling the chemicalenvironments of the anode and cathode enabling use of anode-incompatiblematerials, such as solvents and electrolytes, on the cathode sidewithout deleterious impact on the anode, and vice versa. This broadensthe array of materials that may be used in active metal electrochemicalcells and facilitates cell fabrication while providing a high level ofionic conductivity to enhance performance of an electrochemical cell inwhich the membrane is incorporated.

The membrane may have any suitable composition, for example, it may be amonolithic material chemically compatible with both the anode andcathode environments, or a composite composed of at least two componentsof different materials having different chemical compatibilities, onechemically compatible with the anode environment and the otherchemically compatible with the cathode environment.

Composite membranes may be composed of at least two components ofdifferent materials having different chemical compatibilityrequirements. The composite may be composed of a laminate of discretelayers of materials having different chemical compatibilityrequirements, or it may be composed of a gradual transition betweenlayers of the materials. By “chemical compatibility” (or “chemicallycompatible”) it is meant that the referenced material does not react toform a product that is deleterious to battery cell operation whencontacted with one or more other referenced battery cell components ormanufacturing, handling or storage conditions.

A first material layer of the composite is both ionically conductive andchemically compatible with an active metal electrode material. Chemicalcompatibility in this aspect of the invention refers to a material thatis chemically stable and therefore substantially unreactive whencontacted with an active metal electrode material. Active metals arehighly reactive in ambient conditions and can benefit from a barrierlayer when used as electrodes. They are generally alkali metals such(e.g., lithium, sodium or potassium), alkaline earth metals (e.g.,calcium or magnesium), and/or certain transitional metals (e.g., zinc),and/or alloys of two or more of these. The following active metals maybe used: alkali metals (e.g., Li, Na, K), alkaline earth metals (e.g.,Ca, Mg, Ba), or binary or ternary alkali metal alloys with Ca, Mg, Sn,Ag, Zn, Bi, Al, Cd, Ga, In. Preferred alloys include lithium aluminumalloys, lithium silicon alloys, lithium tin alloys, lithium silveralloys, and sodium lead alloys (e.g., Na₄Pb). A preferred active metalelectrode is composed of lithium. Chemical compatibility also refers toa material that may be chemically stable with oxidizing materials andreactive when contacted with an active metal electrode material toproduce a product that is chemically stable against the active metalelectrode material and has the desirable ionic conductivity (i.e., afirst layer material). Such a reactive material is sometimes referred toas a “precursor” material.

A second material layer of the composite is substantially impervious,ionically conductive and chemically compatible with the first material.By substantially impervious it is meant that the material provides asufficient barrier to battery electrolytes and solvents and otherbattery component materials that would be damaging to the electrodematerial to prevent any such damage that would degrade electrodeperformance from occurring. Thus, it should be non-swellable and free ofpores, defects, and any pathways allowing air, moisture, electrolyte,etc. to penetrate though it to the first material. Preferably, thesecond material layer is so impervious to ambient moisture, carbondioxide, oxygen, etc. that an encapsulated lithium alloy electrode canbe handled under ambient conditions without the need for elaborate drybox conditions as typically employed to process other lithiumelectrodes. Because the composite protective layer described hereinprovides such good protection for the lithium (or other active metal),it is contemplated that electrodes and electrode/electrolyte compositesof this invention may have a quite long shelf life outside of a battery.Thus, the invention contemplates not only batteries containing anegative electrode, but unused negative electrodes andelectrode/electrolyte laminates themselves. Such negative electrodes andelectrode/electrolyte laminates may be provided in the form of sheets,rolls, stacks, etc. Ultimately, they may be integrated with otherbattery components to fabricate a battery. The enhanced stability of thebatteries of this invention will greatly simplify this fabricationprocedure.

In addition to the protective composite laminate structure describedabove, a protective composite in accordance with the present inventionmay alternatively be a functionally graded layer, as further describedbelow.

It should be noted that the first and second materials are inherentlyionically conductive. That is, they do not depend on the presence of aliquid electrolyte or other agent for their ionically conductiveproperties.

Additional layers are possible to achieve these aims, or otherwiseenhance electrode stability or performance. All layers of the compositehave high ionic conductivity, at least 10⁻⁷ S/cm, generally at least10⁻⁶ S/cm, for example at least 10⁻⁵ S/cm to 10⁻⁴ S/cm, and as high as10⁻³ S/cm or higher so that the overall ionic conductivity of themulti-layer protective structure is at least 10⁻⁷ S/cm and as high as10⁻³ S/cm or higher.

Protective Membranes and Structures

FIG. 1 is a conceptual illustration of an ionically conductiveprotective membrane in accordance with the present invention in contextas it would be used in an active metal/aqueous battery cell 120, such asa lithium/water, lithium/air or lithium/metal hydride battery cell, inaccordance with the present invention. The membrane 100 is bothionically conductive and chemically compatible with an active metal(e.g., lithium) electrode (anode) 106 on one side, and substantiallyimpervious, ionically conductive and chemically compatible with acathode structure 110 having an electronically conductive component, anionically conductive component, and an electrochemically activecomponent, with at least one cathode structure component being orincluding an aqueous constituent. The ionic conductivity of the membraneis at least 10⁻⁷ S/cm, generally at least 10⁻⁶ S/cm, for example atleast 10⁻⁵ S/cm to 10⁻⁴ S/cm, and as high as 10⁻³ S/cm or higher. Theactive metal anode 106 in contact with the first side of the protectivemembrane is connected with a current collector 108 composed of aconductive metal, such as copper, that is generally inert to and doesnot alloy with the active metal. The electronically conductivecomponent, for example in Li/water and Li/air cells, a porous catalyticelectronically conductive support, not shown in this conceptualdepiction, is generally provided adjacent to the protective membrane onthe cathode, provides electron transport from the anode (via a cathodecurrent collector 112) and facilitates electroreduction of the cathodeactive material.

The protective membrane may be a composite composed of two or morematerials that present sides having different chemical compatibility tothe anode and electrolyte and/or cathode, respectively. The composite iscomposed of a first layer of a material that is both ionicallyconductive and chemically compatible with an active metal electrodematerial. The composite also includes second layer of a material that issubstantially impervious, ionically conductive and chemically compatiblewith the first material and the cathode/electrolyte environment.

As described further below, given the protection afforded by theprotective membranes of the present invention, the electrolytes and/orcathodes combined with the protected anodes of the present invention mayinclude a wide variety of materials including, but not limited to, thosedescribed in the patents of PolyPlus Battery Company, referenced hereinbelow.

FIG. 2A illustrates a protective membrane composite battery separator inaccordance with one embodiment of the present invention. The separator200 includes a laminate of discrete layers of materials with differentchemical compatibilities. A layer of a first material or precursor 202is ionically conductive and chemically compatible with an active metal.In most cases, the first material is not chemically compatible withoxidizing materials (e.g., air, moisture, etc). The first layer, incontact with the active metal, may be composed, in whole or in part, ofactive metal nitrides, active metal phosphides, active metal halides oractive metal phosphorus oxynitride-based glasses. Specific examplesinclude Li₃N, Li₃P, LiI, LiBr, LiCl and LiF. In at least one instance,LiPON, the first material is chemically compatible with oxidizingmaterials. The thickness of the first material layer is preferably about0.1 to 5 microns, or 0.2 to 1 micron, for example about 0.25 micron.

As noted above, the first material may also be a precursor materialwhich is chemically compatible with an active metal and reactive whencontacted with an active metal electrode material to produce a productthat is chemically stable against the active metal electrode materialand has the desirable ionic conductivity (i.e., a first layer material).Examples of suitable precursor materials include metal nitrides, redphosphorus, nitrogen and phosphorus containing organics (e.g., amines,phosphines, borazine (B₃N₃H₆), triazine (C₃N₃H₃)) and halides. Somespecific examples include P (red phosphorus), Cu₃N, SnN_(x), Zn₃N₂,FeN_(x), CoN_(x), aluminum nitride (Al₃N), silicon nitride (Si₃N₄) andI₂, Br₂, Cl₂ and F₂. Such precursor materials can subsequently reactwith active metal (e.g., Li) to form Li metal salts, such as the lithiumnitrides, phosphides and halides described above. In some instances,these first layer material precursors may also be chemically stable inair (including moisture and other materials normally present in ambientatmosphere), thus facilitating handling and fabrication. Examplesinclude metal nitrides, for example Cu₃N.

Also, a suitable active metal compatible layer may include a polymercomponent to enhance its properties. For example, polymer-iodinecomplexes like poly(2-vinylpyridine)-iodine (P2VP-I₂),polyethylene-iodine, or with tetraalkylammonium-iodine complexes canreact with Li to form a LiI-based film having significantly higher ionicconductivity than that for pure LiI.

The ionic conductivity of the first material is high, at least 10⁻⁷S/cm, generally at least about 10⁻⁵ S/cm, and may be as high as 10⁻³S/cm or higher.

Adjacent to the first material or precursor layer 202 is a second layer204 that is substantially impervious, ionically conductive andchemically compatible with the first material or precursor andenvironments normally corrosive to the active metal of the anode,including glassy or amorphous metal ion conductors, such as aphosphorus-based glass, oxide-based glass, phosphorus-oxynitride-basedglass, sulpher-based glass, oxide/sulfide based glass, selenide basedglass, gallium based glass, germanium-based glass or boracite glass(such as are described D. P. Button et al., Solid State Ionics, Vols.9-10, Part 1, 585-592 (December 1983); ceramic active metal ionconductors, such as lithium beta-alumina, sodium beta-alumina, Lisuperionic conductor (LISICON), Na superionic conductor (NASICON), andthe like; or glass-ceramic active metal ion conductors. Specificexamples include LiPON, Li₃PO₄.Li₂S.SiS₂, Li₂S.GeS₂.Ga₂S₃, Li₂O.11Al₂O₃,Na₂O.11Al₂O₃, (Na, Li)_(1+x)Ti_(2-x)Al_(x)(PO₄)₃ (0.6≦x≦0.9) andcrystallographically related structures, Na₃Zr₂Si₂PO₁₂, Li₃Zr₂Si₂PO₁₂,Na₅ZrP₃O₁₂, Na₅TiP₃O₁₂, Na₃Fe₂P₃O₁₂, Na₄NbP₃O₁₂, Li₅ZrP₃O₁₂, Li₅TiP₃O₁₂,Li₃Fe₂P₃O₁₂ and Li₄NbP₃O₁₂, and combinations thereof, optionallysintered or melted. Suitable ceramic ion active metal ion conductors aredescribed, for example, in U.S. Pat. No. 4,985,317 to Adachi et al.,incorporated by reference herein in its entirety and for all purposes.

A particularly suitable glass-ceramic material for the second layer ofthe protective composite is a lithium ion conductive glass-ceramichaving the following composition:

Composition mol % P₂O₅ 26-55% SiO₂ 0-15% GeO₂ + TiO₂ 25-50% in whichGeO₂ 0-50% TiO₂ 0-50% ZrO₂ 0-10% M₂O₃ 0-10% Al₂O₃ 0-15% Ga₂O₃ 0-15% Li₂O3-25%and containing a predominant crystalline phase composed ofLi_(1+x)(M,Al,Ga)_(x)(Ge_(1-y)Ti_(y))_(2-x)(PO₄)₃ where X≦0.8 and0≦Y≦1.0, and where M is an element selected from the group consisting ofNd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb and/orLi_(1+x+y)Q_(x)Ti_(2-x)Si_(y)P_(3-y)O₁₂ where 0<X≦0.4 and 0<Y≦0.6, andwhere Q is Al or Ga. The glass-ceramics are obtained by melting rawmaterials to a melt, casting the melt to a glass and subjecting theglass to a heat treatment. Such materials are available from OHARACorporation, Japan and are further described in U.S. Pat. Nos.5,702,995, 6,030,909, 6,315,881 and 6,485,622, incorporated herein byreference.

The high conductivity of some of these glasses, ceramics andglass-ceramics (ionic conductivity in the range of about 10⁻⁷ to 10⁻³S/cm or greater) may enhance performance of the protected lithium anode,and allow relatively thick films to be deposited without a large penaltyin terms of ohmic resistance.

Either layer may also include additional components. For instance, asuitable active metal compatible layer (first layer) may include apolymer component to enhance its properties. For example, polymer-iodinecomplexes like poly(2-vinylpyridine)-iodine (P2VP-I₂),polyethylene-iodine, or tetraalkylammonium-iodine complexes can reactwith Li to form a LiI-based film having significantly higher ionicconductivity than that for pure LiI. Also, a suitable first layer mayinclude a material used to facilitate its use, for example, the residueof a thin wetting layer (e.g., Ag) used to prevent reaction betweenvapor phase lithium (during deposition) and LiPON when LiPON is used asa first layer material.

In addition, the layers may be formed using a variety of techniques.These include deposition or evaporation (including e-beam evaporation)or thermal spray techniques such as plasma spray of layers of material,such as Li₃N or an ionically conductive glass (e.g., LiPON). Also, asnoted above, the active metal electrode adjacent layer may be formed insitu from the non-deleterious reaction of one or more precursors withthe active metal electrode. For example, a Li₃N layer may be formed on aLi anode by contacting Cu₃N with the Li anode surface, or Li₃P may beformed on a Li anode by contacting red phosphorus with the Li anodesurface.

Such compositions, components and methods for their fabrication aredescribed in U.S. Provisional Patent Application No. 60/418,899, filedOct. 15, 2002, titled IONICALLY CONDUCTIVE COMPOSITES FOR PROTECTION OFANODES AND ELECTROLYTES, its corresponding U.S. patent application Ser.No. 10/686,189 (Attorney Docket No. PLUSP027), filed Oct. 14, 2003, andtitled IONICALLY CONDUCTIVE COMPOSITES FOR PROTECTION OF ACTIVE METALANODES, and U.S. patent application Ser. No. 10/731,771 (Attorney DocketNo. PLUSP027X1), filed Dec. 5, 2003, and titled IONICALLY CONDUCTIVECOMPOSITES FOR PROTECTION OF ACTIVE METAL ANODES. These applications areincorporated by reference herein in their entirety for all purposes.

The composite barrier layer should have an inherently high ionicconductivity. In general, the ionic conductivity of the composite is atleast 10⁻⁷ S/cm, generally at least about 10⁻⁶ to 10⁻⁵ S/cm, and may beas high as 10⁻⁴ to 10⁻³ S/cm or higher. The thickness of the firstprecursor material layer should be enough to prevent contact between thesecond material layer and adjacent materials or layers, in particular,the active metal of the anode with which the separator is to be used.For example, the first material layer may have a thickness of about 0.1to 5 microns; 0.2 to 1 micron; or about 0.25 micron.

The thickness of the second material layer is preferably about 0.1 to1000 microns, or, where the ionic conductivity of the second materiallayer is about 10⁻⁷ S/cm, about 0.25 to 1 micron, or, where the ionicconductivity of the second material layer is between about 10⁻⁴ about10⁻³ S/cm, about 10 to 1000 microns, preferably between 1 and 500microns, and more preferably between 10 and 100 microns, for example 20microns.

When the first material layer is a precursor material chemically stablein air, for example Cu₃N or LiPON, the protective composite batteryseparator may be handled or stored in normal ambient atmosphericconditions without degradation prior to incorporation into a batterycell. When the separator is incorporated into a battery cell, theprecursor layer 202 is contacted with an active metal (e.g., lithium)electrode. The precursor reacts with the active metal to form anionically conductive material that is chemically compatible with theactive metal electrode material. The second layer is contacted with anelectrolyte to which a cathode and current collector is or has beenapplied. Alternatively, the second layer acts as the sole electrolyte inthe battery cell. In either case, the combination of the two layers inthe protective composite protects the active metal electrode and theelectrolyte and/or cathode from deleterious reaction with one another.

In addition to the protective composite laminates described above, aprotective composite in accordance with the present invention mayalternatively be compositionally and functionally graded, as illustratedin FIG. 2B. Through the use of appropriate deposition technology such asRF sputter deposition, electron beam deposition, thermal spraydeposition, and or plasma spray deposition, it is possible to usemultiple sources to lay down a graded film. In this way, the discreteinterface between layers of distinct composition and functionalcharacter is replaced by a gradual transition of from one layer to theother. The result, as with the discrete layer composites describedabove, is a bi-functionally compatible ionically conductive composite220 stable on one side 214 to lithium or other active metal (firstmaterial), and on the other side 216 substantially impervious and stableto ambient conditions, and ultimately, when incorporated into a batterycell, to the cathode, other battery cell components (second material).In this embodiment, the proportion of the first material to the secondmaterial in the composite may vary widely based on ionic conductivityand mechanical strength issues, for example. In many, but not all,embodiments the second material will dominate. For example, suitableratios of first to second materials may be 1-1000 or 1-500, for exampleabout 1 to 200 where the second material has greater strength and ionicconductivity than the first (e.g., 2000 Å of LiPON and 20-30 microns ofa glass-ceramic such as described herein). The transition betweenmaterials may occur over any (e.g., relatively short, long orintermediate) distance in the composite. Other aspects of the inventionapply to these graded protective composites substantially as to thediscrete-layered laminate protective composites, for example, they maybe used in the electrode and cell embodiments, etc.

FIG. 3A illustrates an encapsulated anode structure incorporating aprotective laminate composite in accordance with the present invention.The structure 300 includes an active metal electrode 308, e.g., lithium,bonded with a current collector 310, e.g., copper, and a protectivecomposite 302. The protective composite 302 is composed of a first layer304 of a material that is both ionically conductive and chemicallycompatible with an active metal electrode material, but not chemicallycompatible with electrolyte or oxidizing materials (e.g., air). Forexample, the first layer, in contact with the active metal, may becomposed, in whole or in part, of active metal nitrides, active metalphosphides or active metal halides. Specific examples include Li₃N,Li₃P, LiI, LiBr, LiCl and LiF. The thickness of the first material layeris preferably about 0.1 to 5 microns, or 0.2 to 1 micron, for exampleabout 0.25 micron.

Active metal electrode materials (e.g., lithium) may be applied to thesematerials, or they may be formed in situ by contacting precursors suchas metal nitrides, metal phosphides, metal halides, red phosphorus,iodine and the like with lithium. The in situ formation of the firstlayer may be by way of conversion of the precursors to a lithiatedanalog, for example, according to reactions of the following type (usingP, Cu₃N, and PbI₂ precursors as examples):

1. 3Li+P=Li₃P (reaction of the precursor to form Li-ion conductor);

2(a). 3Li+Cu₃N=Li₃N+3Cu (reaction to form Li-ion conductor/metalcomposite);

2(b). 2Li+PbI₂=2LiI+Pb (reaction to form Li-ion conductor/metalcomposite).

First layer composites, which may include electronically conductivemetal particles, formed as a result of in situ conversions meet therequirements of a first layer material for a protective composite inaccordance with the present invention and are therefore within the scopeof the invention.

A second layer 306 of the protective composite is composed of asubstantially impervious, ionically conductive and chemically compatiblewith the first material or precursor, including glassy or amorphousmetal ion conductors, such as a phosphorus-based glass, oxide-basedglass, phosphorus-oxynitride-based glass, sulpher-based glass,oxide/sulfide based glass, selenide based glass, gallium based glass,germanium-based glass or boracite glass; ceramic active metal ionconductors, such as lithium beta-alumina, sodium beta-alumina, Lisuperionic conductor (LISICON), Na superionic conductor (NASICON), andthe like; or glass-ceramic active metal ion conductors. Specificexamples include LiPON, Li₃PO₄.Li₂S.SiS₂, Li₂S.GeS₂.Ga₂S₃, Li₂O.11Al₂O₃,Na₂O.11Al₂O₃, (Na, Li)_(1+x)Ti_(2−x)Al_(x)(PO₄)₃ (0.6≦x≦0.9) andcrystallographically related structures, Na₃Zr₂Si₂PO₁₂, Li₃Zr₂Si₂PO₁₂,Na₅ZrP₃O₁₂, Na₅TiP₃O₁₂, Na₃Fe₂P₃O₁₂, Na₄NbP₃O₁₂, Li₅ZrP₃O₁₂, Li₅TiP₃O₁₂,Li₃Fe₂P₃O₁₂ and Li₄NbP₃O₁₂, and combinations thereof, optionallysintered or melted. Suitable ceramic ion active metal ion conductors aredescribed, for example, in U.S. Pat. No. 4,985,317 to Adachi et al.,incorporated by reference herein in its entirety and for all purposes.Suitable glass-ceramic ion active metal ion conductors are described,for example, in U.S. Pat. Nos. 5,702,995, 6,030,909, 6,315,881 and6,485,622, previously incorporated herein by reference and are availablefrom OHARA Corporation, Japan.

The ionic conductivity of the composite is at least 10⁻⁷ S/cm, generallyat least 10⁻⁶ S/cm, for example at least 10⁻⁵ S/cm to 10⁻⁴ S/cm, and ashigh as 10⁻³ S/cm or higher. The thickness of the second material layeris preferably about 0.1 to 1000 microns, or, where the ionicconductivity of the second material layer is about 10⁻⁷ S/cm, about 0.25to 1 micron, or, where the ionic conductivity of the second materiallayer is between about 10⁻⁴ about 10⁻³ S/cm, 10 to 1000 microns,preferably between 1 and 500 micron, and more preferably between 10 and100 microns, for example 20 microns.

When the anode structure is incorporated in a battery cell with a wateror air cathode, the first layer 304 is adjacent to an active metal(e.g., lithium) anode and the second layer 306 is adjacent to cathodematerial and its associated aqueous electrolyte. As further describedbelow, such battery cells also generally include a porous catalyticelectronically conductive support structure to facilitate the cathodicreaction in the cell.

As noted above with regard to the protective membrane separatorstructures described in connection with FIGS. 2A and B, in addition tothe protective composite laminates described above, a protectivecomposite in accordance with the present invention may alternatively becompositionally and functionally graded, as illustrated in FIG. 3B.Through the use of appropriate deposition technology such as RF sputterdeposition, electron beam deposition, thermal spray deposition, and orplasma spray deposition, it is possible to use multiple sources to laydown a graded film. In this way, the discrete interface between layersof distinct composition and functional character is replaced by agradual transition of from one layer to the other. The result, as withthe discrete layer composites described above, is a bi-functionallycompatible ionically conductive composite 320 stable on one side 314 tolithium or other active metal (first material), and on the other side316 substantially impervious and stable to the cathode, other batterycell components and preferably to ambient atmosphere (second material).

As noted with reference to the graded separator in FIG. 2B, in thisembodiment the proportion of the first material to the second materialin the composite may vary widely based on ionic conductivity andmechanical strength issues, for example. In many, but not all,embodiments the second material will dominate. For example, suitableratios of first to second materials may be 1-1000 or 1-500, for exampleabout 1 to 200 where the second material has greater strength and ionicconductivity than the first (e.g., 2000 Å of LiPON and 20-30 microns ofa glass-ceramic such as described herein). The transition betweenmaterials may occur over any (e.g., relatively short, long orintermediate) distance in the composite.

Also, an approach may be used where a first material and second materialare coated with another material such as a transient and/or wettinglayer. For example, a glass-ceramic plate such as described herein (e.g.from OHARA Corp.) is coated with a LiPON layer, followed by a thinsilver (Ag) coating. When lithium is evaporated onto this structure, theAg is converted to Ag—Li and diffuses, at least in part, into thegreater mass of deposited lithium, and a protected lithium electrode iscreated. The thin Ag coating prevents the hot (vapor phase) lithium fromcontacting and adversely reaction with the LiPON first material layer.After deposition, the solid phase lithium is stable against the LiPON. Amultitude of such transient/wetting (e.g., Sn) and first layer materialcombinations can be used to achieve the desired result.

A protective membrane in accordance with the present invention may beformed using a variety of methods. These include deposition orevaporation. Protective membrane composites of the present invention maybe formed by deposition or evaporation (including e-beam evaporation) ofthe first layer of material or precursor on the second layer ofmaterial. Also, as noted above and described further below, the firstlayer may be formed in situ from the non-deleterious reaction of one ormore precursors with an active metal electrode or material, bydeposition or evaporation of lithium on the precursor, by direct contactof the precursor with a lithium metal (e.g., foil), or by plating of theprecursor with lithium through a second layer material. In someembodiments, the second layer material may also be formed on the firstlayer material, as described further below.

Referring to FIG. 4A, a first method for forming a protective membranecomposite in accordance with the present invention is shown. A firstlayer, that is a highly ionically conductive active metal chemicallycompatible material, is directly deposited onto a second layer material,that is a substantially impervious, ionically conductive material, forexample, a highly ionically conductive glass or glass-ceramic materialsuch as LiPON or a glass-ceramic material described above. This can bedone by a variety of techniques including RF sputtering, e-beamevaporation, thermal evaporation, or reactive thermal or e-beamevaporation, for example. In the particular example illustrated in thefigure, lithium is evaporated in a nitrogen plasma to form a lithiumnitride (Li₃N) layer on the surface of a glass-ceramic material such asthe glass-ceramic material described above. This is followed byevaporation of lithium metal onto the Li₃N film. The Li₃N layerseparates the lithium metal electrode from the second material layer,but allows Li ions to pass from the Li electrode through the glass. Ofcourse, other active metal, and first and second layer materials, asdescribed herein, may be used as well.

Alternatively, referring to FIG. 4B, a second method for forming aprotective membrane composite in accordance with the present inventionis shown. The ionically conductive chemically compatible first layermaterial is formed in situ following formation of a precursor layer onthe second layer material. In the particular example illustrated in thefigure, a surface of a glass-ceramic layer, for example one composed ofthe a glass-ceramic material described above, is coated with redphosphorus, a precursor for an active metal (in this case lithium)phosphide. Then a layer of lithium metal is deposited onto thephosphorus. The reaction of lithium and phosphorus forms Li₃P accordingto the following reaction: 3Li+P=Li₃P. Li₃P is an ionically conductivematerial that is chemically compatible with both the lithium anode andthe glass-ceramic material. In this way, the glass-ceramic (or othersecond layer material) is not in direct contact with the lithiumelectrode. Of course, other active metal, first layer precursor andsecond layer materials, as described herein, may be used as well.Alternative precursor examples include Cu₃N, which may be formed as athin layer on a second layer material (e.g., glass-ceramic) andcontacted with a Li anode in a similar manner according to the followingreaction: 3Li+Cu₃N=Li₃N+3 Cu; or lead iodide which may be formed as athin layer on a polymer electrolyte and contacted with a Li anode in asimilar manner according to the following reaction: 2Li+PbI₂=2 LiI+Pb.

In another alternative, illustrated in FIG. 5, a protective membranecomposite in accordance with the present invention may alternatively becompositionally and functionally graded so that there is a gradualtransition of from one layer to the other. For example, a plasma sprayoperation with two spray heads, one for the deposition of a firstcomponent material, such as Li₃N, Cu₃N, Li₃P, LiPON, or otherappropriate material, and the other for the deposition of a secondcomponent material, such as an glass-ceramic, for example as availablefor OHARA Corp., may be used. The first plasma spray process beginslaying down a layer of pure glass-ceramic material, followed by agradual decrease in flow as the second plasma spray torch is graduallyturned on, such that there is a gradient from pure glass-ceramic to acontinuous transition from glass-ceramic to pure LiPON or Li₃N, etc. Inthis way, one side of the membrane is stable to active metal (e.g.,lithium, sodium, etc.) and the other side is substantially imperviousand stable to the cathode, other battery cell components and preferablyto ambient conditions. Electron beam deposition or thermal spraydeposition may also be used. Given the parameters described herein, oneor skill in the art will be able to use any of these techniques to formthe graded composites of the invention.

To form a protected anode, lithium is then bonded to the graded membraneon the first layer material (stable to active metal) side of the gradedprotective composite, for example by evaporation of lithium onto theprotective composite as described above. It may also be desirable to adda bonding layer on top of the lithium stable side of the gradedcomposite protective layer, such as Sn, Ag, Al, etc., before applyinglithium.

In any of the forgoing methods described with reference to FIGS. 4A-Band 5, rather than forming a lithium (or other active metal) layer onthe first layer material or precursor, the first layer material orprecursor of the protective composite may be contacted with the lithiumby bonding metallic lithium to the protective interlayer material orprecursor, for example by direct contact with extruded lithium metalfoil.

In a further embodiment, a suitable substrate, e.g., having a wettinglayer, such as a film of tin on copper, may be coated with a first layermaterial precursor, e.g., Cu₃N. This may then be coated with a secondlayer material, e.g., a (ionically) conductive glass. An active metalelectrode may then be formed by plating the tin electrode with lithium(or other active metal), through the first and second layer materials.The Cu₃N precursor is also converted to Li₃N by this operation tocomplete the protective composite in accordance with the presentinvention on a lithium metal electrode. Details of an active metalplating process are described in commonly assigned U.S. Pat. No.6,402,795, previously incorporated by reference.

With regard to the fabrication methods described above it is importantto note that commercial lithium foils are typically extruded and havenumerous surface defects due to this process, many of which have deeprecesses that would be unreachable by line-of-sight depositiontechniques such as RF sputter deposition, thermal and E-beamevaporation, etc. Another issue is that active metals such as lithiummay be reactive to the thin-film deposition environment leading tofurther deterioration of the surface during the coating process. Thistypically leads to gaps and holes in a membrane deposited onto thesurface of an active metal electrode. However, by inverting the process,this problem is avoided; lithium is deposited on the protective membranerather than the protective membrane being deposited on lithium. Glass,and glass-ceramic membranes can be made quite smooth either bymelt-casting techniques, cut and polish methods, or a variety of knownmethods leading to smooth surfaces (lithium is a soft metal that cannotbe polished). Single or multiple smooth, gap-free membranes may then bedeposited onto the smooth surface. After deposition is complete, activemetal can be deposited onto the smooth surface by evaporation, resultingin an active metal/protective membrane interface that is smooth andgap-free. Alternatively, a transient bonding layer such as Ag can bedeposited onto the protective membrane such that extruded lithium foilcan be joined to the membrane by pressing the foil against the Ag layer.

Also as noted above, in an alternative embodiment of the invention thefirst layer may include additional components. For instance, a suitablefirst layer may include a polymer component to enhance its properties.For example, polymer-iodine complexes like poly(2-vinylpyridine)-iodine(P2VP-I₂), polyethylene-iodine, or tetraalkylammonium-iodine can reactwith Li to form an ionically conductive LiI-based film that ischemically compatible with both an active metal and a second layermaterial as described herein. Without intending to be bound by theory,it is expected that the use of polymer-iodine charge transfer complexescan lead to formation of composites containing LiI and polymer andhaving significantly higher ionic conductivity than that for pure LiI.Other halogens may also be used in this manner, for example in brominecomplexes.

Referring to FIG. 6A, a first embodiment of this aspect of the presentinvention is shown. A polymer layer and a layer of iodine are coated ona second layer material surface and allowed to react formingpolymer-iodine complex.

According to this method, a thin layer of polymer may be applied to thesecond material layer (e.g., conductive glass) using brushing, dipping,or spraying. For example, a conductive glass layer may be coated with athin (e.g, 0.5 to 2.0 micron, preferably 0.1 to 0.5 micron) layer ofP2VP in this way.

One technique for applying an iodine coating is sublimation ofcrystalline iodine that can be achieved at room temperature (e.g., about20 to 25° C.) in a reactor placed in the dry box or in a dry room. Asublimed layer of iodine can be made very thin (e.g., 0.05 to 1.0microns and the rate of sublimation can be adjusted by varying thetemperature or distance between the substrate and source of iodine.

Alternatively, high concentrations (e.g., 50 to 100 g/liter of iodinecan be dissolved in an organic solvent, such as acetonitrile andn-heptane. Dissolved iodine can be coated on the conductive glasssurface by such methods as dip coating, spraying or brushing, amongothers. In this case, treatment conditions can be easily changed byvarying the length of coating treatment and iodine concentrations.Examples of iodine sources for this technique include metal iodides areAgI and PbI₂, which are known to be used as the cathode materials insolid-state batteries with Li anode and LiI-based solid electrolyte.

Then, lithium (or other active metal) is contacted with thepolymer-iodine complex on the conductive glass (or other second layermaterial), for example by evaporation or pressing onto the glass coatedwith this complex. The result is a LiI-containing composite protectivebarrier layer on the Li anode.

Referring to FIG. 6B, an alternative embodiment of this aspect of thepresent invention is shown. A conductive glass (or other second layermaterial) surface is coated with a thin layer of iodine, such as by atechnique described above, that can react with Li forming LiI layer (A).

Active metal, for example lithium foil, can be coated with a thin layerof polymer (B), for example as described above, and then contacted withthe iodine layer on the glass. After assembly, iodine reacts with thepolymer layer and, as a result, LiI-containing composite protectivebarrier layer with reduced impedance is formed.

The protected anode structures with fully-formed protective layers andbattery separators incorporating ambient stable precursors describedabove may be handled or stored in normal ambient atmospheric conditionswithout degradation prior to incorporation into a battery cell.

Active Metal/Aqueous Cells

The protected active metal anodes described herein enable theconstruction of active metal battery and other electrochemical cellshaving aqueous constituents in their cathodes, such as Li/water cells,Li/air cells and Li/metal hydride cells. Generally, such cells have acathode structure comprising an electronically conductive component, anionically conductive component, and an electrochemically activecomponent, with at least one of these cathode structure componentshaving an aqueous composition or constituent. These cells have greatlyenhanced performance characteristics relative to conventional cells. Asdescribed further below, the cells have a broad array of potentialimplementations and applications. While these cell types operateaccording to different electrochemical reactions and haveelectrochemically active components in their cathodes drawn fromdifferent states (primarily liquid, gas and solid states, respectively),each of these cell types includes the common feature of an aqueousconstituent for Li ion transport on the cathode side of the cell. Thedecoupling of the anode and cathode by the protective membrane allowsfor the fabrication of this powerful new type of battery or otherelectrochemical cell.

Active Metal/Water Cells

The present invention provides novel active metal/water battery andother electrochemical cells. These cells have an active metal, e.g.,alkali metal, e.g., lithium (Li), anode with a protective membrane and acathode structure with an aqueous electrochemically active component,for example water or aqueous peroxide solutions. The anode side of thesecells is described above. In a cell, any part of the active metalelectrode that is not covered by the protective membrane will generallybe sealed off from the aqueous cathode environment, such as by a currentcollector material (e.g., copper), an o-ring seal, a crimp seal, polymeror epoxy sealant, or combination of these.

The cathode side of these cells includes a cathode structure with anelectronically conductive component, an ionically conductive component,and at least an aqueous electrochemically active component. The aqueouselectrochemically active component of these cells frequently has nativeionic conductivity so that a single solution may act as both theelectrochemically active component and the ionically conductivecomponent. As described further with reference to specific embodimentsbelow, the cells have an electronically conductive support structureelectrically connected with the anode to allow electron transfer toreduce the cathode material (e.g., H₂O in a Li/water cell). Theelectronically conductive support structure is generally porous to allowfluid flow and either catalytic (e.g., Ni, Pt) or treated with acatalyst to catalyze the reduction of the cathode material. An aqueouselectrolyte with suitable ionic conductivity is generally in contactwith the electronically conductive support structure to allow iontransport through the electronically conductive support structure tocomplete the redox reaction.

The electronically conductive support structure may also be treated withan ionomer, such as per-fluoro-sulfonic acid polymer film (e.g., du PontNAFION) to expand the range of acceptable aqueous electrochemicallyactive components to those having little or no native ionicconductivity. An additional advantage of ionomers like NAFION is thatthe salt is chemically bonded to the polymer backbone, and thereforecannot be flushed out in flow-through or open cell implementations,described below.

The battery cells may be primary or secondary cells. For primary cells,the cathode side of the cells may be open to the environment and theoxidized lithium on the cathode side of the cell may simply disperseinto the environment. Such a cell may be referred to as an “open” cell.Cells for marine applications which use sea water as anelectrochemically active and ionically conductive material are anexample. For secondary cells, the oxidized lithium is retained in areservoir on the cathode side of the cell to be available to rechargethe anode by moving the Li ions back across the protective membrane whenthe appropriate potential is applied to the cell. Such a cell may bereferred to as a “closed” cell. Such closed cells require venting forthe hydrogen produced at the cathode. Appropriate battery cell vents areknown in the art.

An example of an active metal/water battery cell in accordance with thepresent invention is a lithium/water battery cell, as conceptuallyillustrated above in FIG. 1. FIG. 7 illustrates a specificimplementation of such a lithium/water battery cell in accordance withthe present invention. The battery cell 700 includes a lithium negativeelectrode (anode) 702. Alternatively, another active metal, particularlyan alkali metal, may be used. The lithium metal electrode can be bondedto a lithium ion conductive protective membrane 704 according to any ofthe techniques described herein and in the patent applicationsincorporated by reference, as described above, with or without the useof a bond coat such as a thin layer of Ag or other suitable alloyingmetal, depending upon the technique used. The cell also includes acathode structure composed of a porous catalytic electronicallyconductive support structure 706, a electrochemically active material(e.g., water) and an aqueous electrolyte 708 (e.g., salt water, oraqueous solutions of LiCl, LiBr, LiI, NH₄Cl, NH₄Br, etc. may act as boththe electrochemically active component and the ionically conductivecomponent; or, as noted below, in the case where ionomers are used,little or no salt may be needed). In some implementations, an optionalseparator (not shown) may be provided between the protective membrane704 and the porous catalytic electronically conductive support structure706. This separator may be useful to protect the protective membranefrom the possibility of being damaged by any roughness on the porouscatalytic electronically conductive support structure 706 and mayprovide a fluid reservoir for the aqueous cathode activematerial/electrolyte. It may be composed of a polyolefin such aspolyethylene or polypropylene, for example a CELGARD separator. Itshould be understood that in this cell the electrochemically activecomponent (water) and the ionically conductive component (aqueouselectrolyte) will be intermixed in a single solution and are thus shownas the single element 708.

As noted above, on the cathode side of the protective membrane, the cellincludes a cathode structure with an electronically conductivecomponent, an aqueous and/or ionomeric ionically conductive component,and at least an aqueous electrochemically active component. In oneembodiment these components are represented by an aqueous electrolyte708 and a porous catalytic electronically conductive support structure706. The electrochemically active material in a Li/water battery iswater. While not so limited, the electrochemical reaction between the Liions from the anode and the water is believed to be described by thefollowing reaction scheme:

Li+H₂O=LiOH+1/2H₂.

Thus, for every mol of Li and water reacted, a mol of LiOH and one halfmol of hydrogen gas is produced.

The cell's aqueous electrolyte provides ion carriers for transport(conductivity) of Li ions and anions that combine with Li. As notedabove, the electrochemically active component (water) and the ionicallyconductive component (aqueous electrolyte) will be intermixed as asingle solution, although they are conceptually separate elements of thebattery cell. Suitable electrolytes for the Li/water battery cell of theinvention include any aqueous electrolyte with suitable ionicconductivity. Suitable electrolytes may be acidic, for example, strongacids like HCl, H₂SO₄, H₃PO₄ or weak acids like acetic acid/Li acetate;basic, for example, LiOH; neutral, for example, sea water, LiCl, LiBr,LiI; or amphoteric, for example, NH₄Cl, NH₄Br, etc

The suitability of sea water as an electrolyte enables a battery cellfor marine applications with very high energy density. Prior to use, thecell structure is composed of the protected anode and the porouselectronically conductive support structure (electronically conductivecomponent). When needed, the cell is completed by immersing it in seawater which provides the electrochemically active and ionicallyconductive components. Since the latter components are provided by thesea water in the environment, they need not transported as part of thebattery cell prior to it use (and thus need not be included in thecell's energy density calculation). Such a cell is referred to as an“open” cell since the reaction products on the cathode side are notcontained. Such a cell is, therefore, a primary cell.

Secondary Li/water cells are also possible in accordance with theinvention. As noted above, such cells are referred to as “closed” cellssince the reaction products on the cathode side are contained on thecathode side of the cell to be available to recharge the anode by movingthe Li ions back across the protective membrane when the appropriaterecharging potential is applied to the cell.

As noted above and described further below, in another embodiment of theinvention, ionomers coated on the porous catalytic electronicallyconductive support reduce or eliminate the need for ionic conductivityin the electrochemically active material.

The electrochemical reaction that occurs in a Li/water cell is a redoxreaction in which the electrochemically active cathode material getsreduced. In a Li/water cell, the catalytic electronically conductivesupport facilitates the redox reaction. As noted above, while not solimited, in a Li/water cell, the cell reaction is believed to be:

Li+H₂O═LiOH+1/2H₂.

The half-cell reactions at the anode and cathode are believed to be:

Anode: Li═Li⁺+e⁻

Cathode: e⁻+H₂O═OH⁻+1/2H₂

Accordingly, the catalyst for the Li/water cathode promotes electrontransfer to water, generating hydrogen and hydroxide ion. A common,inexpensive catalyst for this reaction is nickel metal; precious metalslike Pt, Pd, Ru, Au, etc. will also work but are more expensive.

Also considered to be within the scope of Li (or other activemetal)/water batteries of this invention are batteries with a protectedLi anode and an aqueous electrolyte composed of gaseous and/or solidoxidants soluble in water that can be used as active cathode materials(electrochemically active component). Use of water soluble compounds,which are stronger oxidizers than water, can significantly increasebattery energy in some applications compared to the lithium/waterbattery, where during the cell discharge reaction, electrochemicalhydrogen evolution takes place at the cathode surface. Examples of suchgaseous oxidants are O₂, SO₂ and NO₂. Also, metal nitrites, inparticular NaNO₂ and KNO₂ and metal sulfites such as Na₂SO₃ and K₂SO₃are stronger oxidants than water and can be easily dissolved in largeconcentrations. Another class of inorganic oxidants soluble in water areperoxides of lithium, sodium and potassium, as well as hydrogen peroxideH₂O₂.

The use of hydrogen peroxide as an oxidant can be especially beneficial.There are at least two ways of utilizing hydrogen peroxide in a batterycell in accordance with the present invention. First of all, chemicaldecomposition of hydrogen peroxide on the cathode surface leads toproduction of oxygen gas, which can be used as active cathode material.The second, perhaps more effective way, is based on the directelectroreduction of hydrogen peroxide on the cathode surface. Inprincipal, hydrogen peroxide can be reduced from either basic or acidicsolutions. The highest energy density can be achieved for a batteryutilizing hydrogen peroxide reduction from acidic solutions. In thiscase a cell with Li anode yields E⁰=4.82 V (for standard conditions)compared to E⁰=3.05 V for Li/Water couple. However, because of very highreactivity of both acids and hydrogen peroxide to unprotected Li, suchcell can be practically realized only for protected Li anode inaccordance with the present invention.

In order to increase efficiency of hydrogen peroxide reduction on thecathode surface, especially at high discharge rates, electrolyte flowcan be used in lithium/water cells with dissolved hydrogen peroxide. Inthis case hydrogen peroxide plays a role of a fuel continuously suppliedto the cathode surface. High energy density cells for marineapplications having a protected Li anode in accordance with the presentinvention can utilize hydrogen peroxide dissolved in sea water andcontinuously flowing through the cell.

Active Metal/Air Battery Cells

Active metal/air battery cells are another class of active metal/aqueouscells in accordance with the present invention. These cells have anactive metal, e.g., alkali metal, e.g., lithium (Li), anode with aprotective membrane and a cathode structure with air as theelectrochemically active component. While not so limited, theelectrochemical reaction between the Li ions from the anode and the airis believed to be described by one or more of the following reactionschemes:

Li+1/2H₂O+1/4O₂═LiOH

Li+1/4O₂=1/2Li₂O

Li1/2O=1/2Li₂O₂

Thus both moisture (H₂O) and oxygen in the air are participants in theelectrochemical reaction.

The anode side of these cells is the same as for any of the activemetal/aqueous cells provided herein, and is described above. In a cell,any part of the active metal electrode that is not covered by theprotective membrane will generally be sealed off from the air cathodeenvironment, such as by a current collector material (e.g., copper), ano-ring seal, a crimp seal, polymer or epoxy sealant, or combination ofthese.

The cathode side of these cells includes a cathode structure with anelectronically conductive component, an ionically conductive component,and air as an electrochemically active component. The airelectrochemically active component of these cells includes moisture toprovide water for the electrochemical reaction. As described furtherwith reference to specific embodiments below, the cells have anelectronically conductive support structure electrically connected withthe anode to allow electron transfer to reduce the air cathode activematerial. The electronically conductive support structure is generallyporous to allow fluid (air) flow and either catalytic or treated with acatalyst to catalyze the reduction of the cathode active material. Anaqueous electrolyte with suitable ionic conductivity or ionomer is alsoin contact with the electronically conductive support structure to allowion transport within the electronically conductive support structure tocomplete the redox reaction.

One example of a Li/air battery cell in accordance with the presentinvention is illustrated in FIG. 8. In the embodiment, the cell 800includes an active metal negative electrode (anode) 808, e.g., lithium,bonded with a current collector 810, e.g., copper, and a laminateprotective membrane composite 802. As described above, a protectivemembrane composite laminate 802 is composed of a first layer 804 of amaterial that is both ionically conductive and chemically compatiblewith an active metal electrode material, and a second layer 806 composedof a material substantially impervious, ionically conductive andchemically compatible with the first material and an aqueousenvironment. The cell also includes a cathode structure (sometimesreferred to as an “air electrode”) 812 with an electronically conductivecomponent, an aqueous and/or ionomeric ionically conductive component,and air as the electrochemically active component. As with the Li/watercells, in some implementations, an optional separator (not shown) may beprovided between the protective membrane 802 and the cathode structure.This separator may be useful to protect the protective membrane from thepossibility of being damaged by any roughness on the cathode structure812, which may be a porous catalytic electronically conductive supportstructure, as described further below. In the case of Li/air batterieswith acidic electrolyte, the separator can improve cell capacitydelivered before the electrolyte converts into a basic solution due tothe cell discharge reaction and, accordingly, becomes reactive toatmospheric CO₂ (carbonation reaction). It may be composed of apolyolefin such as polyethylene or polypropylene, for example a CELGARDseparator.

The cathode structure 812 includes an electronically conductivecomponent (for example, a porous electronic conductor, an ionicallyconductive component with at least an aqueous constituent, and air as anelectrochemically active component. It may be any suitable airelectrode, including those conventionally used in metal (e.g., Zn)/airbatteries or low temperature (e.g., PEM) fuel cells. Air cathodes usedin metal/air batteries, in particular in Zn/air batteries, are describedin many sources including “Handbook of Batteries” (Linden and T. B.Reddy, McGraw-Hill, NY, Third Edition) and are usually composed ofseveral layers including an air diffusion membrane, a hydrophobic Teflonlayer, a catalyst layer, and a metal electronically conductivecomponent/current collector, such as a Ni screen. The catalyst layeralso includes an ionically conductive component/electrolyte that may beaqueous and/or ionomeric. A typical aqueous electrolyte is composed ofKOH dissolved in water. An typical ionomeric electrolyte is composed ofa hydrated (water) Li ion conductive polymer such as aper-fluoro-sulfonic acid polymer film (e.g., du Pont NAFION). The airdiffusion membrane adjusts the air (oxygen) flow. The hydrophobic layerprevents penetration of the cell's electrolyte into the air-diffusionmembrane. This layer usually contains carbon and Teflon particles. Thecatalyst layer usually contains a high surface area carbon and acatalyst for acceleration of reduction of oxygen gas. Metal oxides, forexample MnO₂, are used as the catalysts for oxygen reduction in most ofthe commercial cathodes. Alternative catalysts include metal macrocyclessuch as cobalt phthalocyanine, and highly dispersed precious metals suchat platinum and platinum/ruthenium alloys. Since the air electrodestructure is chemically isolated from the active metal electrode, thechemical composition of the air electrode is not constrained bypotential reactivity with the anode active material. This can allow forthe design of higher performance air electrodes using materials thatwould normally attack unprotected metal electrodes.

Since metal/air batteries obtain the cathode active reactant from theambient environment, the volumetric and gravimetric energy densities arevery high. The high energy density of metal/air batteries makes themattractive for a wide variety of applications where weight and size area premium. Unfortunately, conventional metal/air batteries suffer fromparasitic reactions in which the metal electrode corrodes to generatehydrogen. The anode corrosion reaction can be minimized by incorporatingKOH in the electrolyte. However, this introduces another problem as CO₂from the air is converted to K₂CO₃ in the air electrode, thereby formingprecipitates that cause premature failure of the cell. Such problems areeliminated by the subject invention in that the active metal electrodeis isolated from the aqueous electrolyte, preventing corrosion of theanode. Since the anode does not corrode in the electrolyte solution, andis in fact de-coupled from it, the air electrode can be formulated withneutral (LiCl), basic (KOH), or acidic (NH₄Cl, HCl, etc.) electrolyte.While not so limited, for the case of acidic electrolyte, shown below,the cell reaction is believed to proceed by forming lithium chloride. Insuch a cell, the air electrode does not scavenge CO₂ from the air, andthere is no K₂CO₃ formation.

Li+1/2O2+NH₄Cl=LiCl+NH₃

The subject invention allows the use of neutral or acidic electrolytesin active metal/air batteries due to the fact that the aqueouselectrolyte is not in contact with the metal anode, and thereby cannotcorrode the metal anode.

The Li/air cells of the present invention may be either primary orsecondary cells.

Active Metal/Metal Hydride Battery Cell

Another type of active metal/aqueous battery cell incorporating aprotected anode and a cathode structure with an aqueous component inaccordance with the present invention is a lithium (or other activemetal)/metal hydride battery, as illustrated in FIG. 9. For example,protected lithium anodes as described herein can be discharged andcharged in aqueous solutions suitable as electrolytes in a lithium/metalhydride battery. Suitable electrolytes provide a source or protons.Examples include aqueous solutions of halide acids or acidic salts,including chloride or bromide acids or salts, for example HCl, HBr,NH₄Cl or NH₄Br.

During discharge, lithium ions from the anode pass through the ionicallyconductive protective membrane into the aqueous electrolyte, and protonsare reduced to hydride ions that are incorporated into the metal alloypositive electrode (cathode). Thus, the cathode side of the cell has acathode structure an electronically conductive component (metal alloy),an ionically conductive component (aqueous electrolyte), and anelectrochemically active component (protons/metal alloy). This isanalogous to known metal hydride chemistry used in nickel/metal hydride(Ni/MH) batteries. However, in this case the acid in the electrolyte isconsumed and converted to lithium salt. The cells may be primary, butare generally secondary (rechargeable) due to materials costs. Onrecharge of secondary cells, lithium ions are transported through theprotective membrane to the lithium electrode and reduced to Li metal,while the metal hydride is oxidized to release protons and regeneratethe acid electrolyte. Such a cell exhibits excellent cycle life due tothe highly reversible nature of the positive and negative electrodes.

While not so limited, the half and full cell reactions for alithium/metal hydride cell in accordance with the present invention arebelieved to be as follows:

Anode: Li═Li⁺+e⁻

Cathode: HCl+M+e⁻═MH+Cl⁻

Cell Reaction: Li+HCl+M═LiCl+MH

Metal hydride alloys are well known to those skilled in the art, and aregenerally chosen from rare earth based alloys (Misch metal) designatedas AB₅ (LaNi₅ and LaCo₅ with partial substitutions to improveperformance) and AB₂ alloys consisting of titanium and zirconium (suchas ZrNi₂). The metal hydride electrode is typically engineered as ahighly porous structure having a perforated nickel foil or grid ontowhich a polymer-bonded active hydrogen storage alloy is coated. Themetal hydride electrode is used commercially in the nickel/metal hydride(Ni/MH) battery. In this chemistry, an alkaline electrolyte is used, andthe hydride alloys are modified to perform well in alkaline conditions.For the case of a Li/MH battery, the electrolyte will be acidic, and sothe composition of the AB₅ or AB₂ alloy may be modified to cycle well inacidic electrolytes.

Li/Water Battery and Hydrogen Generator for Fuel Cell

The use of protective layers on active metal electrodes in accordancewith the present invention allows the construction of active metal/waterbatteries that have negligible corrosion currents, described above. TheLi/water battery has a very high theoretical energy density of 8450Wh/kg. The cell reaction is Li+H₂O═LiOH+1/2H₂. Although the hydrogenproduced by the cell reaction is typically lost, in this embodiment ofthe present invention it is used to provide fuel for an ambienttemperature fuel cell. The hydrogen produced can be either fed directlyinto the fuel cell or it can be used to recharge a metal hydride alloyfor later use in a fuel cell. At least one company, Millenium Cell,makes use of the reaction of sodium borohydride with water to producehydrogen. However, this reaction requires the use of a catalyst, and theenergy produced from the chemical reaction of NaBH₄ and water is lost asheat.

NaBH₄+2H₂O→4H₂+NaBO₂

When combined with the fuel cell reaction, H₂+O₂═H₂O, the full cellreaction is believed to be:

NaBH₄+2O₂→2H₂O+NaBO₂

The energy density for this system can be calculated from the equivalentweight of the NaBH₄ reactant (38/4=9.5 grams/equiv.). The gravimetriccapacity of NaBH₄ is 2820 mAh/g; since the voltage of the cell is about1, the specific energy of this system is 2820 Wh/kg. If one calculatesthe energy density based on the end product NaBO₂, the energy density islower, about 1620 Wh/kg.

In the case of the Li/water cell, the hydrogen generation proceeds by anelectrochemical reaction believed described by:

Li+H₂O═LiOH+1/2H₂

In this case, the energy of the chemical reaction is converted toelectrical energy in a 3 volt cell, followed by conversion of thehydrogen to water in a fuel cell, giving an overall cell reactionbelieved described by:

Li+1/2H₂O+1/4O₂═LiOH

where all the chemical energy is theoretically converted to electricalenergy. The energy density based on the lithium anode is 3830 mAh/g at acell potential of about 3 volts which is 11,500 Wh/kg (4 times higherthan NaBH₄). If one includes the weight of water needed for thereaction, the energy density is then 5030 Wh/kg. If the energy densityis based on the weight of the discharge product, LiOH, it is then 3500Wh/kg, or twice the energy density of the NaBO₂ system. This can becompared to previous concepts where the reaction of lithium metal withwater to produce hydrogen has also been considered. In that scenario theenergy density is lowered by a factor of three, since the majority ofthe energy in the Li/H₂O reaction is wasted as heat, and the energydensity is based on a cell potential for the H₂/O₂ couple (as opposed to3 for Li/H₂O) which in practice is less than one. In this embodiment ofthe present invention, illustrated in FIG. 10, the production ofhydrogen can also be carefully controlled by load across the Li/waterbattery, the Li/water battery has a long shelf life due to theprotective membrane, and the hydrogen leaving the cell is alreadyhumidified for use in the H₂/air fuel cell.

Catalytic Electronically Conductive Support Structures for Li/water andLi/air Cells

Any suitable catalytic electronically conductive support structuresufficiently porous so that surface area is maximized without limitingmass transfer of the electrochemically active material may be used inthe Li/water and Li/air cells of the present invention. Suitable poroussupport materials include those that are inherently electronicallyconductive and those that are treated (e.g., coated) to becomeelectronically conductive. Supports composed of a porous material thatis not electronically conductive (but possibly ionically conductive)include alumina, silica glass, ceramics, glass-ceramics and water-stablepolymers. The insulating support is metallized in order to carrycurrent. Insulating supports can be metallized by a process known aselectroless deposition in which a catalyst and reducing agent areadsorbed onto the surface of the insulator before exposing it to asolution of metal ions in solution which are reduced to metal on thesurface according to techniques known in the art. Typical metal coatingsare copper and nickel. Nickel is particularly preferred for itscatalytic properties (particularly in Li/water cells).

Suitable glass, ceramic, and glass-ceramic supports can be an inertmaterial, or made from an ionically conductive material such as aresuitable for the protective membrane described herein. The poroussupport may be made through tape-casting or extrusion of a glass orceramic or glass-ceramic powder/polymer binder/solvent mixture. Onto theporous support a second layer of finer glass or ceramic or glass-ceramicpowder could be laid down by tape-casting or extrusion such that whenthe two-layer article is fired, the coarse support layer retainsporosity while the thin-film densifies completely to become the acomponent of the protective membrane. Alternatively, the support layercould be pre-fired, and then a thin-film laid down by tape-casting orextrusion, and fired to full density.

A glass, ceramic or glass-ceramic component of the protective membranecan also be applied by melt-spray techniques, such as plasma-spray andvacuum plasma-spray, or other thermal spray techniques; such films mayalso need heat treatment as described as described in the publicationJie Fu, J. Amer. Ceram. Soc., 80 [7] p. 1901-1903 (1997) and the patentsof OHARA Corp., previously cited and incorporated by reference herein,to improve the ionic conductivity of the solid In such processes, themembrane material may be supplied to a plasma torch nozzle as a powder,and sprayed out of the nozzle as fine molten droplets. The moltendroplets hit the substrate and solidify. In this manner, a glass,ceramic or glass-ceramic film can be directly deposited onto dense orporous substrates to produce either a porous or dense film, depending onoperating parameters.

Suitable polymeric supports include polyethylene, polypropylene, Kevlar,Nylon, etc. As an example, a thin glass-ceramic layer may be tape-castand fired to full density. Then the polymeric support would be depositedonto the glass-ceramic film by tape-casting of a polymer/binder/solventfilm, and allowed to dry.

Suitable inherently electronically conductive supports included co-firedand pre-fired metals. A porous stainless steel support may be fabricatedthrough tape-casting or extrusion. Onto the porous support, a thin glassor glass-ceramic layer could be deposited by tape-casting. The 2-layerstructure could then be fired at low temperature (e.g., <900° C.) inair, or at higher temperatures under reducing conditions (e.g., H₂furnace) to minimize oxidation of the stainless steel support duringsintering. A porous nickel support could be fabricated as describedabove, but would have to be fired under reducing conditions to preventoxidation of Ni to NiO. Alternatively, the porous support is pre-firedto the desired porosity. A second layer of glass-ceramic could beapplied to the porous support by tape-casting, aerosol-spray coating,electrophoretic deposition, etc. Since the substrate will not sinterduring firing (since it is pre-sintered), the film will undergoconstrained sintering (constrained by a non-sintering substrate). Sincethe film is a glass and can flow during firing, this is not a problem.

Non-catalytic porous supports are impregnated with a catalyst tofacilitate the reduction of water for reaction with the Li ions from theanode that pass through the protective layer.

In the case of the nickel support, the nickel surface is catalytic forthe reduction of water, and so, catalyst impregnation is probablyunnecessary for that application.

Sample Cell Fabrication, Components and Configurations

Deposition Technique for Cell Fabrication

FIG. 11 depicts the fabrication of a thin-film Li/water or Li/airbattery using plasma-spray and other deposition techniques in accordancewith one embodiment of the present invention. A laminate protectivecomposite membrane is formed on a porous nickel catalytic electronicallyconductive support. Then lithium metal is deposited on the protectivemembrane. An advantage of using plasma-spray is that the substrate canbe maintained at a relatively low temperature; so, for example theporous nickel support will at a sufficiently low temperature (belowabout 500° C.) that the conversion of Ni to NiO is prevented. The porousNi support is then covered with a thin glass or glass-ceramic membraneby plasma-spray. A subsequent lithium compatible layer of LiPON or othersuitable materials such as Cu₃N is deposited onto the glass membrane bysuitable technique, such as ebeam evaporation, RF sputtering, CVD, orplasma-spray. Onto the lithium compatible layer, it may be desirable todeposit a thin Ag transient coating by vacuum evaporation, as describedabove. Finally, a lithium electrode is either evaporated onto theassembly (i.e. Li/Ag/LiPON/Ni), or mechanically bonded to the assemblyby pressing.

The cell will be completed when needed by the subsequent addition ofwater and electrolyte to the porous electronically conductive support,for example by immersing it in seawater or other aqueous electrolyticsolution. In the actual battery cell, the lithium metal electrode willbe isolated from the seawater environment by means of a hermetic sealthat may be composed of elastomeric or epoxy resins.

The catalytic electronically conductive support may also be treated withan ionomer, such as per-fluoro-sulfonic acid polymer film (e.g., du PontNAFION) to expand the range of acceptable electrolytes to those havinglittle or no native ionic conductivity.

The porous catalytic electronically conductive support may also bestructurally reinforced with a metal frame to enhance its rigidity andstrength. The frame may be composed of any suitable metal, such asstainless steel or aluminum. In a particular embodiment, the frame maybe arranged in a grid pattern, such as that illustrated below in FIGS.12. B and D.

Supported Protective Membrane Structure and Fabrication

The use of thin protective membranes is desirable for several reasonsincluding reducing materials costs, reducing weight and thereforeincreasing energy density and facilitating ion transport through themembrane. In order to use the thinnest possible protective membranelayer for a Li/aqueous cell, a thin ionically conductive glass-ceramic(for example) film is produced by an appropriate technique, such astape-casting. Film thicknesses of a few microns to many microns are wellknown to those skilled in the art of tape-casting, and such films areroutinely used in multi-layer ceramic capacitors. The ionicallyconducting glass-ceramic is tape-cast and then fired to full density.The 10 to 50 micron film is still fragile at this point.

In another embodiment, the thin glass or glass-ceramic membrane could bemade by “draw-down” techniques as described by Sony Corporation andShott Glass (T. Kessler, H. Wegener, T. Togawa, M. Hayashi, and T.Kakizaki, “Large Microsheet Glass for 40-in. Class PALC Displays,” 1997,FMC2-3, downloaded from Shott Glass website, incorporated herein byreference. In essence, the glass is handled in the molten state whichallows the drawing of thin ribbons of glass. If the cooling rate of theglass sheet exceeds the crystallization rate, then the glass will beessentially amorphous. Since many of Nasicon-type glasses require thepresence of a crystalline phase for high conductivity, it may benecessary to heat treat the thin glass sheets to allow crystallizationof the conductive phase and formation of a “glass-ceramic” as describedin the publication Jie Fu, J. Amer. Ceram. Soc., 80 [7] p. 1901-1903(1997) and the patents of OHARA Corp., previously cited and incorporatedby reference herein, to improve the ionic conductivity of the solid. Theprocess of crystallization (devitrification of the amorphous state) mayalso lead to surface roughness. Accordingly, the heat treatment may haveto be optimized to promote small grained morphology, or a furtherchemical or mechanical polishing of the surface may be needed.

The thin glass-ceramic membrane produced by either technique can then beattached to an electronically conductive porous support (e.g. metal ormetallized as described above) by adhesive bonding (e.g., with epoxy,elastomeric, and/or ceramic adhesives) or firing in an oven for example.One example of this approach is illustrated in FIGS. 12A-E. A metalframe has open areas filled with porous catalytic electronicallyconductive support material for the Li/water redox reaction. In thisway, the thin glass-ceramic film is supported by the metal frame that isa porous, catalytic for water reduction, and electronically conductivesupport structure.

In a second embodiment, porous catalytic electronically conductivesupport such as nickel foam is bonded directly onto the thinglass-ceramic protective membrane component, and the glass-ceramic/porous catalytic electronically conductive support element is theneither bonded or placed on the metal frame support. Such structures canalso be made in a symmetric arrangement, as shown in FIG. 12E, toimprove the strength of the structure and maximize the air electrodearea.

In yet another embodiment, the glass membrane itself is strengthenedthrough use of a grid pattern imposed on the glass by a “waffle”-typemold. To do this, the molten glass can be injected or pressed into anappropriate mold to impose reinforcing ridges into the glass, whilemaintaining a thin membrane between the ridges. If necessary the“waffle” can then be heat-treated, as described above, to improve theionic conductivity of the solid. The “waffle” type solid electrolyte canthen be bonded to the porous nickel electrode.

Elastomeric Seals

FIG. 13 shows an embodiment in accordance with the present invention inwhich a plurality of glass, ceramic or glass-ceramic ionicallyconductive protective plates are bonded into an array by elastomericseals. In this manner the array has some conformability due to theelastomeric nature of the plate-to-plate seals. The plates may alreadybe bonded to a porous catalytic electronically conductive substrate, andthen lithium (or other active metal) could be deposited on the otherside of the plates to form an anode and complete the solid state portionof the cell (the cathode/electrolyte being in the liquid state).Alternatively, complete solid state portions of cells could also bebonded together as shown in FIG. 13.

Tubular Construction

FIG. 14 shows a tubular construction embodiment of a Li/water or Li/aircell in accordance with the present invention. For example a porousnickel tube could be used as a support. An ionically conductive glass,ceramic or glass-ceramic film such as described herein could bedeposited by a variety of techniques, on either the outside (A) orinside (B) of the tube. The tube could be closed or open ended. Forexample, an open ended tube may be used, and an ionically conductiveglass-ceramic plasma-sprayed onto the outer surface, followed by thelithium compatible first component material (e.g., LiPON), a bond coat(e.g., Ag), and a lithium electrode, and finally a copper foil and endseals. The tube could be suspended in seawater, and used as a highenergy density battery. Depending on whether the lithium is outside ofthe tube, or inside the tube as a central core, the seawater (or air inthe case of a Li/air cell) will flow through the center of the tube oraround the tube, respectively.

Capillary Construction

FIG. 15 shows a capillary construction embodiment of a Li/water orLi/air cell in accordance with the present invention. In this approach,thin diameter glass, ceramic or glass-ceramic capillaries are blown froma protective membrane material. The inner (or outer) surface is coatedwith by the lithium compatible first component material (e.g.,LiPON(Ag)), and molten lithium is wicked into the capillary to form ahigh surface area protected anode fiber. Individual fibers are thencoated with the porous catalytic electronically conductive supportmaterial. The high surface area to volume ratio for such fibers allowsfor high rate applications. A number of such fibers can be connected inparallel to create a high power lithium/water battery, and combinationsof parallel bundles can be connected in series to generate highvoltage/high power batteries.

Alternative Embodiments

A number of other rechargeable lithium/aqueous chemistries are possiblein accordance with the present invention. Some examples of these are:

Lithium-Nickel Battery

The nickel electrode, NiOOH, is well known to those skilled in the art,and has been used commercially for many years in rechargeablenickel/cadmium batteries, and more recently in rechargeable nickel/metalhydride batteries.

Anode reaction: Li═Li⁺+e⁻

Cathode reaction: NiOOH+H₂O+e⁻=Ni(OH)₂+OH⁻

Cell reaction: Li+NiOOH+H₂O═Ni(OH)₂+LiOH

The nickel electrode is highly reversible, and the combination of aprotected Li anode with a NiOOH cathode results in a high energydensity, high cycle life battery.

Lithium-Silver Battery

The silver electrode, AgO, is also well known commercially in the Ag/Znbattery; a high rate battery used largely by the military.

Anode reaction: Li═Li⁺+e⁻

Cathode reaction: AgO+H₂O+2e⁻=Ag+2OH⁻

Cell reaction: 4Li+2AgO+2H2O=4LiOH+2Ag

The combination of a lithium anode and silver cathode results in a highrate, rechargeable battery.

Further, a variety of new aqueous battery chemistries enabled by thepresent invention can result from the combination of protected lithiumanodes with transition metal oxides such as iron oxide, lead oxide,manganese oxide and others.

EXAMPLES

The following examples provide details illustrating advantageousproperties of

Li/water battery cells in accordance with the present invention. Theseexamples are provided to exemplify and more clearly illustrate aspectsof the present invention and are in no way intended to be limiting.

Example 1 Li/Water Cell

A series of experiments were performed in which the commercial ionicallyconductive glass-ceramic from OHARA Corporation described above was usedas the outer layer (second composite layer) of a protective membraneagainst the aqueous environment of the electrolyte and cathode (water).These metal oxide Li conductors are stable in aqueous environments, butare unstable to lithium metal. In order to protect the OHARA membraneagainst metallic lithium, LiPON was used. The OHARA plates were in therange of 0.3 to 1 mm in thickness. The LiPON coating was in the range of0.1 to 0.5 microns in thickness, and was deposited onto the OHARA plateby RF sputtering.

On top of the LiPON coating, a thin coating of Ag was formed by vacuumevaporation to prevent the reaction of hot evaporated lithium with theLiPON film. The Ag films were in the range of 200 to 1000 Å inthickness. LiPON can react with highly reactive Li from the vapor phaseduring Li vacuum deposition. Vacuum deposition of a thin film of Ag, Al,Sn or other Li alloy-forming metal onto the glass-ceramic surface canprevent the reaction LiPON surface with Li. The thickness of this metalfilm is from 50 Å to 10000 Å, preferably, from 100 Å to 1000 Å. Inaddition to protection of the first layer material against reaction withLi, a Li alloy-forming metal film can serve two more purposes. In somecases after formation the first layer material the vacuum needs to bebroken in order to transfer this material through the ambient or dryroom atmosphere to the other chamber for Li deposition. The metal filmcan protect the first layer against reaction with components of thisatmosphere. In addition, the Li alloy-forming metal can serve as abonding layer for reaction bonding of Li to the first layer material.When lithium is evaporated onto this structure, the Ag is converted toAg—Li and diffuses, at least in part, into the greater mass of depositedlithium.

Following deposition of the Ag film, approximately 5 microns of lithiummetal were evaporated onto the Ag film, creating a Li(Ag)/LiPON/OHARAprotected lithium electrode. This protected lithium electrode isillustrated in FIG. 16. The protected electrode was fitted into anelectrochemical cell by use of an o-ring such that the OHARA plate wasexposed to an aqueous environment. In one case, the aqueous environmentcomprised a 0.5 M HCl+1.0 M LiCl electrolyte. A platinum counterelectrode was used to facilitate hydrogen reduction when the batterycircuit was completed. An Ag/AgCl reference electrode was used tocontrol potentials of the Li anode and Pt cathode in the cell. Measuredvalues were recalculated into potentials in the Standard HydrogenElectrode (SHE) scale. An open circuit potential (OCP) of 3.05 voltscorresponding closely to the thermodynamic potential difference betweenLi/Li⁺ and H₂/H⁺ in water was observed (FIG. 17). Under normalconditions, one could not observe this potential due to a significantshift of the Li electrode potential in the positive direction caused byintensive corrosion of lithium metal in water. Furthermore, there was novisual indication of reaction of the protected lithium electrode withthe acidic aqueous environment, in particular, any gas evolution and/orLi dissolution. Remarkably, when the circuit was closed, hydrogenevolution was seen immediately at the Pt electrode, indicative of theanode and cathode electrode reactions in the cell, 2Li=2Li+2e⁻, and2H⁺+2e⁻=H₂. The potential-time curves for electrochemical reactions ofLi anodic dissolution and hydrogen cathodic evolution are presented inFIGS. 17 and 18, respectively. This is the first example known where alithium/water battery has been operated in the absence of very largecorrosion currents.

In another analogous experiment, the Li(Ag)/LiPON/OHARA electrode wasused in an aqueous cell having 4 M LiOH electrolyte. In this cell Lialso exhibited the correct OCP value close to the thermodynamicpotential (FIG. 19). This cell was also discharged using a Pt counterelectrode, which immediately evolved hydrogen on closing of the batterycircuit. A small light emitting diode was placed in the Li/water batterycircuit, and it immediately lit up on closing the circuit. Remarkably,reversible cycling of this battery was also possible (FIG. 20), actuallyplating metallic lithium from the aqueous environment during cellcharge. Currents from 1.0 to 15 mA/cm² were used in the cyclingexperiments. As can be seen in FIG. 21, use of high current rates forcycling did not lead to destruction of the anode protective membrane orany irreversible changes in the cell behavior. This is the first knownexample where metallic lithium has been plated with high efficiency froman aqueous electrolyte.

Example 2 Li/Seawater Cell

A lithium/sea (salt) water cell similar to the cell in the Example 1,was built. In this experiment, the Li(Ag)/LiPON/OHARA protected anodewas used in a cell containing a “seawater” as an electrolyte. Theseawater was prepared with 35 ppt of “Instant Ocean” from AquariumSystems, Inc. The conductivity of the seawater used was determined to be4.5 10⁻² S/cm. FIGS. 22A and B show discharge (potential-time) curves atdischarge rates of 0.2 mA/cm² and 0.5 mA/cm², respectively. The resultsindicate an operational cell with good performance characteristics,including a stable discharge voltage. It should be emphasized that inall previous experiments using an unprotected Li anode in seawaterutilization of Li was very poor and at low and moderate currentdensities similar to those used in this example such batteries could notbe used at all due to the extremely high rate of Li corrosion in aseawater (over 19 A/cm²).

Example 3 Li/Seawater Cell with Large Capacity Anode

A lithium/sea (salt) water cell with a Pt wire cathode and a largecapacity Li(Ag)/LiPON/glass-ceramic (OHARA Corp.) protected anode wasbuilt. Following deposition of the Ag film onto the LiPON on the OHARAplate, 50 um thick Li foil from Cyprus Foote Mineral Co. was pressedonto the Ag film to fabricate a thick protected Li anode. A Carverhydraulic press located in a dry room was used for the pressingoperation. The applied pressure was around 800 kg/cm², and duration ofpressing was 10 minutes. The Li surface was polished with a Tyvec fabricjust before pressing onto the Ag film. The Ag film reacted with the Lifoil forming a strong reaction bond. The seawater electrolytecomposition was the same as in the previous example.

FIG. 23 shows a discharge (potential-time) curve at a discharge rate of0.3 mA/cm². The cell exhibited long discharge. Discharge capacitydelivered to the cut-off voltage of 2.0 V corresponded to the Lithickness over 20 μm. This amount of Li could be moved through the Lianode/aqueous electrolyte interface without destruction of theprotective layers.

Example 4 Cell with Protected Li Electrode in Aqueous ElectrolyteContaining Hydrogen Peroxide as a Dissolved Oxidant

A Lithium/Hydrogen Peroxide cell was built with the Li(Ag)/LiPON/OHARAplate protected anode similar to one used in the previous example.Electrolyte was 1M solution of phosphoric acid (H₃PO₄) in water withaddition of 5% hydrogen peroxide (H₂O₂) by weight. The volume of theelectrolyte in the cell was 500 ml. A gold cathode for hydrogen peroxidereduction was made by vacuum coating of both sides of a carbon fiberpaper (35 um thick from Lydall Technical Papers, Rochester, N.Y.) withan approximately 3 um thick Au layer.

FIG. 24 shows a discharge (potential-time) curve for a discharge rate of0.3 mA/cm². The open circuit potential value (OCP) for the cell wasclose to 4.0 V. The cell exhibited a flat discharge potential ofapproximately 3.6 V.

The overall theoretical cell reaction for the Li/H₂O₂ in an acidicmedium is

2Li+H₂O₂=2Li⁺+2H₂O with E⁰=4.82 V (for standard conditions)

Experimentally measured OCP values were lower than the theoretical valuedue to decomposition of hydrogen peroxide to water and oxygen on thecathode surface. As a result, not only hydrogen peroxide, but alsooxygen as well could be reduced on the cathode surface leading todecrease in the OCP and the closed cell potential. Improvements in thecathode structure and use of a cell with flow of electrolyte havingdissolved hydrogen peroxide should significantly improve overall cellcharacteristics. At the same time, the experimental results clearlydemonstrate that using the protected Li anode and a strong oxidantsoluble in water we can build a high energy power source with a veryhigh Li efficiency at low and moderate current rates.

It should be pointed out that acidic electrolytes containing H₂O₂ cannotbe directly used with unprotected Li anode in Li/H₂O₂ cells due to veryhigh rate of Li corrosion and therefore, low Li efficiency.

Example 5 Li/Air Cell with Neutral Electrolyte

A series of experiments were performed whereby a commercial ionicallyconductive glass-ceramic from OHARA Corporation, was used as the outermembrane (second composite layer) against the protic corrosiveenvironment. These metal oxide Li conductors are stable in aqueousenvironments, but are unstable to lithium metal. In order to protect theOHARA membrane against metallic lithium, a variety of materials could beused including LiPON, Cu₃N, SnNx, Li₃N, Li₃P, and metal halides. In thisexperiment, LiPON was used to protect the OHARA plate against reactionwith Li. The OHARA plates were in the range of 0.2 to 0.3 mm inthickness. The LiPON coating was in the range of 0.2 to 0.9 microns inthickness, and was deposited onto the OHARA plate by RF sputtering.

On top of the LiPON coating, a thin Ag film was sputter deposited. Thiswas done to avoid the reaction of hot evaporated lithium with the LiPONfilm. The Ag film was in the range of 200 to 1000 Å in thickness. LiPONcan react with highly reactive Li from the vapor phase during Li vacuumdeposition. Vacuum deposition of a thin film of Ag, Al, Sn or other Lialloy-forming metal onto the glass-ceramic surface can prevent thereaction LiPON surface with Li. The thickness of this metal film is from50 Å to 10000 Å, preferably, from 100 Å to 1000 Å.

Following deposition of the Ag film, approximately 5 microns of lithiummetal were evaporated onto the Ag film, creating a Li(Ag)/LiPON/OHARAprotected anode. The protected anode was fitted into an electrochemicalcell by use of an o-ring such that the OHARA plate was exposed to theaqueous electrolyte environment.

The electrolyte used in this Li/air cell with protected anode was 0.5 MNH₄Cl+0.5 M LiCl. Zirconia cloth from Zircar Products, Inc. was put ontothe OHARA plate and filled with the electrolyte. A volume of theelectrolyte was approximately 0.2 ml. An air electrode made forcommercial Zn/Air batteries was used as a cathode in this experimentalLi/Air cell.

An open circuit potential of 3.25 was observed for this cell. FIG. 25shows discharge (potential-time) curve at discharge rate of 0.3 mA/cm².The cell exhibited discharge voltage of approximately 3.1 V for about1.0 hr (about 3.0 mAh/cm²). This result shows that good performance canbe achieved for Li/air cells with protected Li anode and an electrolytethat does not contain KOH, which is normally employed in existingmetal/Air batteries. KOH slows down corrosion of the metal (e.g., Zn),but draws CO₂ into the cell which causes damaging carbonization. As aresult, conventional metal/air batteries have limited shelf-life. TheLi/air cell described and tested herein is free from negative effect ofelectrolyte carbonization typical for existing metal/air batteries.

Example 6 Li/Air Cell with Large Capacity Anode

A lithium/air cell was built with an air cathode similar to that used inExample 5, but with a Li(Ag)/LiPON/OHARA plate protected anode havingmuch higher capacity. The electrolyte used in this Li/air cell withprotected anode comprised 0.5 M LiOH. Following deposition of the Agfilm onto the LiPON on the OHARA plate, 120 um thick Li foil from CyprusFoote Mineral Co. was pressed onto the Ag film to fabricate a thickprotected Li anode. A Carver hydraulic press located in a dry room wasused for the pressing operation. The applied pressure was around 800kg/cm², and duration of pressing was 10 minutes. The Li surface waspolished with a Tyvec fabric just before pressing onto the Ag film. TheAg film reacted with the Li foil forming a strong reaction bond.

FIG. 26 shows a discharge (potential-time) curve at discharge rate of0.3 mA/cm². The cell exhibited long discharge with a high averagedischarge voltage of 2.9 V. Discharge capacity delivered to the cut-offvoltage of 2.5 V was more than 10 mAh/cm². Remarkably, this large amountof Li corresponding to the Li thickness over 49 μm could be movedthrough the Li anode/aqueous electrolyte interface without destructionof the protective layers.

Example 7 Cycling of Li/Air Cell with Protected Li Anode

A series of experiments were performed in which a commercial ionicallyconductive glass-ceramic from OHARA Corporation, was used as the outer(second) layer of a composite laminate protective layer against theprotic corrosive environment. These metal oxide Li conductors are stablein aqueous environments, but are unstable to lithium metal. In order toprotect the OHARA membrane against metallic lithium, a variety ofmaterials could be used including LiPON, Cu₃N, SnNx, Li₃N, Li₃P, andmetal halides. In the following experiments LiPON was used to protectthe OHARA plate against reaction with Li. The OHARA plates were in therange of 0.2 to 0.3 mm in thickness. The LiPON coating was in the rangeof 0.2 to 0.9 microns in thickness, and was deposited onto the OHARAplate by RF magnetron sputtering.

On top of the LiPON coating, a thin Ag film was sputter deposited. Thiswas done to avoid the reaction of hot evaporated lithium with the LiPONfilm. The Ag films were in the range of 200 to 1000 Å in thickness.LiPON can react with highly reactive Li from the vapor phase during Livacuum deposition. Vacuum deposition of a thin film of Ag, Al, Sn orother Li alloy-forming metal onto the glass-ceramic surface can preventthe reaction LiPON surface with Li. The thickness of this metal film isfrom 50 Å to 10000 Å, preferably, from 100 Å to 1000 Å. In addition toprotection of the first layer material against reaction with Li, a Lialloy-forming metal film can serve two more purposes. In some casesafter formation the first layer material the vacuum needs to be brokenin order to transfer this material through the ambient or dry roomatmosphere to the other chamber for Li deposition. The metal film canprotect the first layer against reaction with components of thisatmosphere. In addition, the Li alloy-forming metal can serve as abonding layer for reaction bonding of Li to the first layer material.When lithium is deposited onto this structure, the Ag is converted toAg—Li and diffuses, at least in part, into the greater mass of depositedlithium.

Following deposition of the Ag film, approximately 5 microns of lithiummetal were evaporated onto the Ag film, creating a Li(Ag)/LiPON/OHARAprotected anode. The protected anode was fitted into an electrochemicalcell by use of an o-ring such that the OHARA plate was exposed to theaqueous environment.

The electrolyte used in this Li/air cell with protected anode wascomprised of 1 M LiOH. The volume of the electrolyte was approximately0.2 ml. An air electrode from commercial Zn/Air batteries was used as acathode in our experimental Li/Air cell.

FIG. 27 shows discharge/charge potential-time curves at discharge/chargerate of 1.0 mA/cm². The duration of each discharge and charge was 3minutes. Even though the air electrodes used in these experiments weredesigned for single discharge, the cell delivered 10 cycles withoutsignificant increase in electrode polarization. This result demonstratesthat a protected Li anode Li/air cell in accordance with the presentinvention can work reversibly.

Conclusion

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. In particular, while the invention is primarilydescribed with reference to a lithium metal anode, the anode may also becomposed of any active metal, in particular, other alkali metals, suchas sodium. It should be noted that there are many alternative ways ofimplementing both the process and compositions of the present invention.Accordingly, the present embodiments are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein.

All references cited herein are incorporated by reference for allpurposes.

1. A battery cell, comprising: an active metal anode having a firstsurface and a second surface; a cathode structure comprising anelectronically conductive component, an ionically conductive component,and an electrochemically active component, wherein at least one cathodestructure component comprises an aqueous constituent; an ionicallyconductive protective membrane on the first surface of the anode, themembrane comprising, one or more materials configured to provide a firstsurface chemically compatible with the active metal of the anode incontact with the anode, and a second surface substantially impervious toand chemically compatible with the cathode structure and in contact withthe cathode structure.
 2. An electrochemical cell structure, comprising:an active metal anode having a first surface and a second surface; aporous catalytic electronically conductive support; an ionicallyconductive protective membrane on the first surface of the anode, themembrane comprising, one or more materials configured to provide a firstsurface chemically compatible with the active metal of the anode, and asecond surface substantially impervious to and chemically compatiblewith the catalytic electronically conductive support, and aqueousenvironments.
 3. A method of making an electrochemical cell structure,comprising: assembling an active metal anode and a cathode structurecomprising an electronically conductive component; wherein a protectivemembrane is disposed between the active metal anode and the cathodestructure, the membrane being ionically conductive and chemicallycompatible with an active metal on a first side, and substantiallyimpervious, ionically conductive and chemically compatible the cathodestructure on the other side; and wherein an active metal material isapplied to the first side of the protective membrane to form the activemetal anode.